1. Field of the Invention
The invention refer primarily to a wind power plant with rotation axis substantially at right angle to wind direction.
2. Description of Related Art
Such exists in several different forms of execution, among them designs with mainly straight wings mounted on bars attached to a vertical axis of rotation. There is also a wind turbine patented by George Darrieus in 1931 consisting of one or more arched wing blades, which rotate around a vertical axis, and are attached at both ends to said axis.
Mankind has for at least two millennia tried to utilize the power of the wind. Wind mills of different designs, and with varying quality, were put to use early, but it was not until the European Middle Ages that windmills useable for grinding grains were designed. Dutch designers succeeded during the 16th century to design wind mills with reasonably high efficiency. These were four-winged with horizontal axis of rotation and an angled transmission to a vertical axis, which powered the grind stones revolving round a vertical axis.
During the 1880ies wind mills with multiple wing blades, still with a horizontal axis of rotation and an angled transmission, where developed in the prairie states of USA for pumping water in the farming districts. This led to an increased interest in using wind powered devices to produce electrical power. During the first decade of the 20 century, there were in Denmark some hundred wind powered electrical generators erected on lattice masts. Up until George Darrieus presented his wind turbine all wind motors were designed with a horizontal axis of rotation on which two or four wings or propeller blades where attached. Utilizing an angled transmission the horizontal rotation where transferred to a vertical axis of rotation, this axis being of necessary length to reach the equipment at ground level, which where to use the rotational power.
Following the 1973 oil crisis there were a renewed interest in using wind power plants, particularly in designs with horizontal axis of rotation, to produce electrical power. Following some twenty years of development there had in the Nordic countries been developed a kind of standard for wind turbines mounted in towers 40-50 meter high, and with a wind turbine having a diameter of approximately the same dimensions.
Wind power plants with a horizontal axis are usually designed for wind speeds up to 12-14 m/s. To make sure that higher wind speeds do not overload the attached electrical generator, the rotational speed of the wind turbine has to be limited. This is usually done either by turning the turbine blades (feathering them) or by designing the turbine blades to stall at high wind speeds.
Irrespective of which design is chosen, it leads to the rotational speed of the wind turbine being limited, and this in combination with the axis of the turbine being equipped with a mechanical break, protect the electric generator from being overloaded.